1. Field of the Invention
The present invention relates to an overvoltage arrester having two frustum-shaped main electrodes which are sealed into the ends of a tubular insulator member and with their planar electrode portions forming active electrode surfaces and facing each other and wherein the tubular insulator is divided at its center by a metallic ring electrode so as to form two discharge paths with the main electrodes.
2. Description of the Prior Art
Over voltage arresters utilizing two symmetrically mounted frustum-shaped electrodes mounted in a sealed manner into opposite ends of a tubular insulator member are well known. Such voltage arresters are called knob arresters and are generally of small dimensions. It is common practice to mount a metallic ring in the center between the frustum-shaped electrodes so as to form a ring electrode in order to form two discharge paths between the ring electrode and the two frustum-shaped electrodes and such over voltage arresters are called two-path over voltage arresters.
It is also known to strengthen the electrodes of an over voltage arrester at the point of the arc initiation so as to obtain good heat removal characteristics. In certain multi-pole over voltage arresters the electrodes are connected to form a part of the wall of the discharge containers so that they may be suitably cooled.
It has also been known in two path arresters to apply a thin layer of particles of a non-conductive or semiconductive material to the main electrodes so as to encourage the start of discharge at a low voltage.